Relative Virulence of Phytophthora Species, Including the Sudden Oak Death Pathogen, P. ramorum, on Leaves of Several Ornamentals
R. G. Linderman1, J. L. Parke2, and E. M. Hansen2
Several Phytophthora species cause leaf and shoot dieback diseases of ornamentals similar to that caused by the Sudden Oak Death pathogen, P. ramorum. Detached leaves of several landscape plants were inoculated with P. ramorum, P. cactorum, P. syringae, P. citricola, P. hevea, P. parasitica, P. citrophthora, and P. cinnamomi. Rhododendron, Pieris, and Laurel were the most susceptible to the most pathogens, based on lesion-severity ratings, with variation depending on the host-pathogen combination. Few hosts were not susceptible to some Phytophthora species, and most pathogens infected some hosts. Necrotic lesions were initially similar, but generally with most pathogens subsequent spread was limited. In contrast, P. ramorum and P. citrophthora lesions spread throughout the entire leaf, suggesting greater virulence and thus underscoring the risk to nursery and landscape plants should the quarantined P. ramorum become more widespread.
1USDA-ARS Horticultural Crops Research Laboratory, Corvallis, OR 97330; (541) 750-8761; lindermr@bcc.orst.edu
2Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331
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